This invention relates to a feedback peak detector fitted wireless handwriting tablet that stands at the key position in analog-digital conversion for enhancing correctness of analog signals by peak sampling and holding to facilitate detection of absolute coordinates of a wireless stylus on a handwriting tablet.
Referring to FIG. 1xe2x80x94a circuit block diagram of a conventional wireless handwriting tabletxe2x80x94a plurality of antennas is distributed in array equidistantly in X-axis and Y-axis direction on both faces of a detector 1 for receiving electromagnetic waves emitted by a wireless stylus 2. A microprocessor 3 is provided to scan all the antennas one after another sequentially and analyze intensity of the signal received to find out to which antenna the stylus 2 is adjacent, then compare the gradients and slopes of the signals of the immediate neighboring antennas to calculate and obtain the absolute coordinates of the wireless stylus 2.
A peak detector 5 plays a key role in the hardware design of the wireless handwriting tablet for receiving analog voltage signals 40 come from a precedent OP amp 4 and sending out peak signals 50 to an Analog/Digital Converter (ADC) 6. Hence, errors may be incurred in A/D conversion and coordinates accordingly in the case of a defective peak detector.
The circuitry of a conventional peak detector may be classified in two categories: one is shown in FIG. 2 and the other in FIG. 3, which are described below.
The one shown in FIG. 2 is defective in a small capacitor C1, which is liable to be charged to an undesirable peak by an instantaneous surge or noise, however, if the capacitor C1 is enlarged improperly, the charging speed will be slowed down to result in amplification deficiency and waveform distortion. The other shown in FIG. 3 is defective that when a MOSFET Q2 is biased by a control pulse signal 30 and turned on or off, a surge is generated to apply upon a capacitor C2, which then holds voltage at a level quite different from that of the precedent circuits to therefore incur jittering and erroneous calculation of the absolute coordinates of the stylus. Besides, a problem of charge/discharge speed is introduced in such a circuit.
The primary object of this invention is to provide a feedback peak detector fitted wireless handwriting tablet, wherein the peak detector is capable of stabilizing peak signals and performing fast charge/discharge to make a stable and correct coordinate calculation and maintain a normal handwriting speed of a wireless tablet.
In order to realize abovesaid object, the peak detector of this invention is composed of: a feedback comparator buffer unit, a peak detection switch unit, a fast charge path unit, a peak signal holding unit, and a fast discharge unit.
For more detailed information regarding advantages or features of this invention, at least an example of preferred embodiment will be elucidated below with reference to the annexed drawings.